湖北快三投注技巧|山东11选5投注技巧|

          
 

 HOME  >>  ENGLISH >> LONG-DISTANCE EDUCATION SERVICE  >> Botany
 

ABSTRACT

            Tea plants are classified as Camellia sinensis variety sinensis and Canmellia sinensis variety assamica (some trees more than 1500 years old are sill thriving in their original forests in Yunnan Province, PRC). The tea plant is kept as an evergreen shrub by pruning When hand picked, only the leaf bud and first two leaves are plucked from the plant. Because of increasing labor costs, mechanieal harvesting is now being used in several countries. In tropical countries, tea leaves are harvested all year around. In temperate countries, harvesting is seasonal.
          In its natural free-growing state, the tea tree can attain a height of 20-30 meters (m). Some trees which are said to be more than 1500 years old are still thriving in thriving flowers and fruits but very few shoots suitable for processing to make tea. In the cultivation of tea on a commercial basis, the height of the plant is maintained at about 1 m for the convenience of manual harvesting of the tender leaves. This control of the height is achieved by pruning at intervals of 2-6 years according to prevailing climatic conditions.
             In 1753, in the binomial system originated by Linnaeus, the tea plant was classified as Thea sinensis. Many synonyms have been given, but now it is generally accepted that the tea plant be classified in the family. Theaceae and in the Camellia species. Many varieties have been proposed, and there are many different qualities arising from different cultivation practices and growing conditions. Camellia sinensis, (L) O. Kuntze, is grown in a very wide range of lautudes, from 45° N(Russia) to 30° (South Africa), and from 150° E (New Guinea) to 60° W (Argentina). According to Sealy (1), there are two main varieties, or jats, Camellia sinensis variety sinensis (Chinese jat) and Camellia sinensis variety assamica (Assam jat). The commercially grown tea plant is generally a highly heterogeneous mixture with contributions from other species of Camellia, such as C. irawadiensis and C. cambodiensis (2). Comprehensive accounts of botany, botanical classification, and physiology of tea have been provided by Barua (3) and Banerjee (4).
              The tea plant is kept as an evergreen shrub by pruning. The leaves are elliptical in shape, Figure I. 1. The  flowers are white with yellow anthers, similar to a wild rose. The tea fruit contains three seeds. When hand picked, only the leaf bud and the first two leaves are plucked from the plant. In some modern, large commercial operations, a battery-powered miniature hedge clipper is used, and the clipped material is collected in an attached bag, Figure I. 2. In some very large operatins, tractor-mounted machinery is used in harvesting tea leaves, Figure I. 3. In such mechanical harvesting methods, more than the first two leaves are often harvested, in contrast to the careful hand-plucking harvesting method.
             In some countries, as in the tropical countries, tea is harvested all around the year. In temperate countries, such as Japan, harvesting is seasonal and each year the new crop is highly prized.
             Propagation of tea plants was originally by seed, and this added to the heterogeneity. More recently (5) vegetative propagation methods have been introduced and are now the accepted method for planting new land and also for replanting or filling in vacancies in existing tea land.
             The choice of the clone for vegetative propagation is dependent on climatic conditions, tolerance to pests and diseases, and the nature of the soil. Attempts are now being made to replace vegetative propagation by tissue culture methods, but these investigations are still in their infancy and it is difficult to predict what other improvements will be developed. Tthere are several hundreds of vegetatively propagated clones with varying characteristics, only a few of which are suitable for commercial cultivation. The basis of selection is by field trials trials to assess yield under different climatic conditions and by evaluation of the quality of the tea samples made from material processed from the field trial plants.
              The annual yield of tea shoot tips is only 1-4 tons per hectare (ha) and is much lower than the yields from vegetative crops such as grassland, forests, and root crops, which yield 10-20 tons/ ha (6). The net annual biomass production of tea plants is 15-18 tons/ ha (7-9), which is comparatively lower than the 25-40 tons/ ha of other vegetative crop plants. Various reasons have been advanced for the lower productivity of tea plants, and among these are: canopy architecture (10), link limitatin (11), and the partition of biomass between woody stems and leaves. This partition of biomass results in a low leaf harvest index of 11% in tea plants as compared with 30%-70% in grassland, forest, and root crop plants. Free-growing tea plants have been observed (12) to produce 50% more dry matter than pruned tea bushes and this may be as much as is produced by grassland and forest species. The low tea harvest yield has been discussed (6) and attributed to low photosynthtic efficiency and partitioning of about half of the dry matter to the frame of the bush, one quarter to the  root system, and only 10% to the harvested shoots, Table I. 1.
             





 
 

本版权系中国茶业协作网所有

http://www.xpfbvp.tw  E-mail: [email protected]

网络支持:?#26412;?#37329;桥网信息技术有限公司  物流配送:?#26412;?#24066;义元商贸中心

湖北快三投注技巧